15-year vs 30-year mortgage: the full tradeoff

The numbers: payment vs. total interest

Same $400,000 loan, realistic rate spread (15-year rates typically run 0.50–0.75 points below 30-year rates):

• 30-year at 7.00%: $2,661/month → ~$558,000 total interest
• 15-year at 6.25%: $3,430/month → ~$217,000 total interest
• Payment difference: +$768/month (+29%)
• Interest saved: ~$341,000

The 15-year's savings come from two compounding forces: a lower rate and half the years of interest accrual. It's the most powerful interest-saving move in home financing — and the most demanding on monthly cash flow.

Why 15-year rates are lower

Lenders charge less for shorter terms because their risk is lower: they get repaid sooner (less inflation erosion), and borrowers who can handle 15-year payments default less often. The 0.50–0.75 point discount is structural, not promotional — it persists across rate environments.

Don't over-credit the rate discount, though. On the $400,000 example, roughly two-thirds of the $341,000 savings comes from the shorter term itself, not the 0.75-point rate edge. Time is the bigger lever.

The flexibility argument: 30-year + invest the difference

The honest case for the 30-year isn't the interest math — it loses that badly. It's optionality:

• Lower mandatory payment: $2,661 is due whether it's a good month or a bad one. Job loss, medical bills, a roof repair — the 30-year survives shocks the 15-year might not.
• Invest the difference: $768/month invested at a 7% average return grows to ~$938,000 over 30 years — dwarfing the $341,000 in interest savings.
• Inflation hedge: the payment is fixed in nominal dollars while your income (hopefully) rises. In real terms, the 30-year payment gets cheaper every year.

There's also a middle truth: the 15-year builds equity dramatically faster. After 5 years, the 15-year borrower owes roughly $296,000 vs. ~$373,000 on the 30-year — a $77,000 equity gap that matters if you need to sell or borrow.

Who should pick which

The 15-year fits when:

• The $3,430 payment (plus taxes and insurance) stays under ~28% of gross income with room to spare.
• You're buying well within your means or refinancing with strong equity.
• You're 10–15 years from retirement and want the mortgage gone before fixed income.
• You value forced savings over flexibility — you'd rather the decision be made for you.

The 30-year fits when:

• The 15-year payment would strain the budget or crowd out retirement contributions (especially any employer match — that's a 50–100% instant return no mortgage beats).
• Income is variable (commission, freelance, business ownership) — the lower mandatory payment is insurance.
• You have higher-return uses for cash: maxing tax-advantaged accounts, business investment.
• You might move within 7–10 years — you'll capture little of the 15-year's back-loaded savings anyway.

The middle path: 30-year loan, 15-year behavior

You can rent the 30-year's safety net while capturing most of the 15-year's savings: take the 30-year at 7.00% and voluntarily pay $3,430/month (the 15-year payment). The loan pays off in ~16.4 years with ~$272,000 in total interest — saving ~$286,000 versus minimum payments.

Compared to a true 15-year loan you give up ~$55,000 (the higher 30-year rate on an accelerated schedule) — the price of the safety valve. In a lean month, you can drop back to $2,661 with no penalty and no refinance. For households with solid but variable income, this hybrid is often the best of both worlds. The requirement, as always: actually making the extra payment, every month.

Common mistakes

Mistake 1: Choosing the 15-year, then struggling

A 15-year payment that leaves no margin turns every surprise into a crisis — and missed mortgage payments damage credit far more than the interest saved. If the payment isn't comfortable, it isn't the right loan.

Mistake 2: Choosing the 30-year, then spending the difference

"Invest the difference" only works if the difference gets invested. Be honest about your track record before counting the $938,000.

Mistake 3: Ignoring the rest of the balance sheet

Accelerating a 6–7% mortgage while skipping a 401(k) match or carrying 20% credit card debt is bad sequencing. Rate-rank every dollar.

Mistake 4: Refinancing into a new 30-year to "get the 15-year later"

Each refinance resets the amortization clock and costs thousands. If the 15-year is the goal and you qualify now, price it now — don't plan a two-step that may never happen.

Mistake 5: Forgetting taxes and insurance

Qualification and affordability run on PITI (principal, interest, taxes, insurance), not P&I. A $3,430 P&I payment is often $4,200+ all-in. Underwrite the full number.

The bottom line

The 15-year wins on interest — ~$341,000 on a $400,000 loan — and the 30-year wins on flexibility. If the higher payment fits comfortably inside your budget with emergency savings intact, take the guaranteed savings. If it doesn't, take the 30-year and either invest the difference with real discipline or pay it like a 15-year and keep the safety valve. The worst choice isn't either term — it's a payment you can't sustain.

Do the math on your loan

Our free mortgage payoff calculator compares 15-year vs. 30-year payments, total interest, and the hybrid "pay a 30-year like a 15-year" strategy on your numbers.

Open the Mortgage Payoff Calculator →

Related calculators

• Mortgage Payoff — how extra payments shorten your loan.
• Refinance Analyzer — does a lower rate actually save you after closing costs?
• Home Equity — lump sum vs. HELOC vs. cash-out refinance.